The disclosure proceeds from a valve assembly and a valve block.
Such a hydraulic valve or control assembly is known in the prior art and comprises so-called “load-sensing” control valves having a control piston for directional and speed control. A metering orifice is formed in the control piston. Here a pressure compensator, which keeps the pressure gradient and therefore also the volumetric flow at the respective metering orifice constant, irrespective of the load, is assigned to a particular control valve. For this purpose the pressure is registered upstream and downstream of the metering orifice and signaled to the pressure compensator. Its piston is biased towards a usually open neutral position by a spring, which exerts an ideally constant force. In addition to the spring the load pressure registered downstream of the metering orifice acts in the opening direction of the piston of the pressure compensator. By contrast only the supply pressure registered upstream of the metering orifice and downstream of the pressure compensator acts in the closing direction of the piston of the pressure compensator.
The load pressure is applied by the load occurring at any given time and cannot be influenced by the control valve; the piston of the pressure compensator on the other hand reacts to load pressure changes and is displaced in the opening direction in the event of an increase in the load pressure or in the closing direction in the event of a fall in the load pressure
The supply pressure is regulated by the pressure compensator and is always high enough to ensure that the force acting in the closing direction due to the supply pressure is in equilibrium with the force of the spring acting in the opening direction and that of the load pressure. The force of the supply pressure thereby always exceeds the force of the load pressure by the constant amount of spring force, thereby resulting in an always constant pressure gradient and consequently a constant volumetric flow at the metering orifice.
The facility for limiting the supply pressure level in order to safeguard the mechanical equipment on the consumer side is also known. This is achieved by allowing a pressure-limiting valve, provided in a load-sensing line, to relay a distorted reading of the actual load pressure to the pressure compensator, in that at a set maximum pressure the pressure-limiting valve opens a connection to the tank, so that the load pressure signaled cannot exceed a specific level. In order to keep the outflow quantity and overall size of the pressure-limiting valve as small as possible, an orifice, through which only a small volumetric flow is able to flow to the tank, is usually arranged in the load-sensing line between the load pick-up and the pressure-limiting valve. The operating principle of this pressure limiter means that the volumetric flow control to the consumer connection of the control valve can be completely disabled. The volumetric flow set by the control piston is fully reduced, for example, if the consumer is being run in opposition to a high resistance, which would require a supply pressure in excess of the set maximum pressure. In this case the supply pressure in the consumer connection will exceed the value set on the pressure-limiting valve by no more than the spring force. Limiting the pressure through multiple pressure-limiting valves for multiple consumer connections is also known.
Such a solution is disclosed by the Rexroth data sheet RD 64276, issue August 2010. In this a valve disk, in which the pressure compensator and the pressure-limiting valve are also arranged, is provided for each control valve. Here the pressure-limiting valve is provided form one consumer. The use of a separate pressure-limiting valve for each of the various actuating devices of the consumer is also disclosed. Disadvantages with this solution are the large amount of space required and the mechanically elaborate design of the valve disk, which leads to high costs.
The Sauer Danvoss data sheet “Series PVG 32, Proportional Valves” proposes to arrange a pressure-reducing valve in a main oil flow. The pressure-reducing valve used for this purpose is of comparatively large design and is designed for a volumetric flow of 200 l/min, for example. A flow passes through the pressure-reducing valve even when no pressure reduction is to ensue, which leads to high pressure losses. In addition, the large overall space required is extremely disadvantageous.
The object of the disclosure, on the other hand, is to create a cost-effective, compact and energy-efficient valve assembly, which serves to limit a supply pressure for all or some hydraulic consumers. A further object of the disclosure is to create a valve block having such a valve assembly, which is of cost-effective and compact design.